Method of heating semiconductor wafers in order to achieve annealing, silicide formation, reflow of glass passivation layers, etc.

ABSTRACT

In accordance with the method, an integrating kaleidoscope and lamps combine to cause heating of a semiconductor wafer to achieve desired effects such as annealing, etc. In one form of the method, the heating of the wafer is such as to achieve rapid annealing by isothermal heating alone. In another form of the method the heating is such as to effect isothermal heating immediately followed by thermal flux heating.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of co-pending patentapplication Ser. No. 584,322, filed Feb. 28, 1984, now abandoned, forApparatus and Method For Heating Semiconductor Wafers In Order ToAchieve Annealing, Silicide Formation, Reflow of Glass PassivationLayers, Etc., inventor Ronald E. Sheets.

The present apparatus and method have important application relative tovarious aspects of the manufacture of semiconductor wafers andintegrated circuits. For example, the apparatus and method will effectreflow of glass passivation layers, and will achieve formation ofsilicides. However, the method portions of the following detaileddescription are directed primarily to the annealing of ion-implantedsemiconductor wafers in order to relieve stresses generated by ionimplantation, in order to fully activate the implanted dopants, and toprovide solid phase epitaxial regrowth so as to restructure damagedcrystal lattices.

BACKGROUND OF THE INVENTION

Semiconductor materials (for example silicon, gallium arsenide, etc.)are at present conventionally implanted with dopants by devices whichutilize high voltages to accelerate ions of the impurities into thesurface of the semiconductors. The amount of penetration of the dopantsis determined by the degree of voltage acceleration of the dopant ions,and is, for example, 0.2 microns. The annealing which necessarilyfollows the ion implantation has, historically, been--and stillis--effected primarily by means of thermal fusion furnaces. Each ofthese is a long quartz tube having a diameter of, for example, fourinches to seven inches, and a length of, for example, four to six feet.Heating coils are wrapped around the tube, and furnace boats are passedtherethrough, each boat containing, for example 30-40 wafers. Thetemperature in the furnace is brought slowly up to a desired level, forexample, 1000° C., following which there is a holding period, followingwhich there is a slow period of cooling. The amount of time required fora semiconductor wafer to be annealed in such a furnace is, typically,30-60 minutes.

There have been major pressures tending toward rapid annealing (shorttime annealing) of large-diameter semiconductor wafers. Many papers andmany patents have been written on the subject of rapid annealing, andvarious approaches have been made. In rapid annealing, it is typical toeffect heating of the wafer to a high temperature in a short period oftime, and then to hold the wafer at the elevated temperature for aboutone to twenty seconds. By keeping the process as short as possible, theimplanted ions do not have time to diffuse into the bulk semiconductormaterial, and circuit speed is maximized. Referring to FIG. 9, theamount of diffusion resulting from certain prior-art rapid annealingprocesses is illustrated by the intermediate curve, which is seen to bevery close to the "as implanted" curve.

It is extremely difficult to achieve effective,commercially-satisfactory rapid annealing of large-diametersemiconductor wafers. Major reasons for the difficulties reside in thecharacteristics of the wafers themselves. Some of these characteristicswill now be mentioned.

The wafers may be four, five or six (or more) inches in diameter, yetare typically only 0.5 millimeters thick. This extreme thinness, incomparison to diameter, means that radiant energy transmitted to oneregion of the wafer will not be thermally conducted, rapidly, to anotherregion thereof. And, as stated below, the heat--instead of beingthermally conducted through the wafer to another region--will bepredominently radiated away from the wafer.

Because of the wafer's size, and because the average specific heat ofsilicon is 1.0 joules per gram, the energy required to heat a siliconwafer to 1000°-1200° C. in a few seconds is substantial. For the typical0.5 mm thick wafer, it requires 145 joules per centimeter squared inorder to bring the temperature to 1200° C. At a temperature of 1200° C.,the water will radiate (lose) 18 watts/cm squared (based on a emissivityof 0.7) over the entire area of the wafer. Thus, as an example, a fourinch wafer will radiate a total of over 2.8 kilowatts when it is at1200° C. In order to hold the wafer at 1200° C., it is necessary for thewafer to continuously absorb 36 watts/centimeter squared for one-sidedheating, or 18 watts/cm² for double-sided heating.

Referring next to the optical properties of the semiconductor materials,it is emphasized that most have a very high index of refraction (3.0 to4.0) in the wavelength range of 0.3 to 4.0 microns, which means that thematerials reflect from 30 to 40 percent of the incident radiation. Thisis many times higher than what would be the case relative to, forexample, glass. Not only is there much reflection, but there is a largeamount of transmission of the radiation through the wafers when they arerelatively cold. From 40-50 percent of the incident radiation in therange from 1.1 to 8 microns is transmitted through the wafer attemperatures below 500°-600° C. Thus, the wafers are radiating,reflecting and transmitting large amounts of energy.

A further characteristic of the wafers is that they are highly subjectto thermal and physical stresses, being easily distorted instead ofremaining flat as desired. Furthermore, regions thereof may tend toripple when thermally shocked.

An additional important characteristic is that relatively long "rapidannealing" tends to reduce adverse effects caused by disuniform heating,that is to say, transmission of radiant energy in differing amounts todifferent regions of the wafer. However, such relatively long "rapidannealing" is not desired, because it slows production and tends toincrease downward diffusion of the dopant and thus reduce circuit speed.

The problems of rapid annealing, and prior-art attempted solutions ofsuch problems, are well summarized by two articles, one of which is:"Rapid Wafer Heating: Status 1983" by Pieter S. Burggraaf (SemiconductorInternational, December, 1983, pp. 69-74). A somewhat less recentoverview is "Short Time Annealing" by T. O. Sedgwick (Journal of theElectrochemical Society: Solid-State Science and Technology, February,1983, pp. 484-493). Both of such articles are hereby incorporated byreference herein.

The Burggraaf article emphasizes the great need for uniformity, stating(p. 70) that" . . . wafer-temperature uniformity is perhaps the mostimportant issue that each vendor has addressed in designing its specificsystem. Wafer-temperature uniformity is important in rapid wafer heatingto minimize slip (crystal dislocation) and wafer flatness distortionsthat occur at high temperature. Wafer-temperature uniformity alsoaffects dopant-activation and junction-depth uniformities. Uniformheating, in fact, is a major challenge in making rapid wafer heating aproduction tool . . . Wafer-temperature uniformity requires that theradiation field be very uniform."

Relative to the mention of junction-depth uniformities in the quotedstatement, it is emphasized that since the wafers are cut up into manyhundreds of elements, and it is important that all of these elements bealike, variations in junction-depth resulting from temperaturedisuniformity are one of the factors which have been adverse to bringingrapid annealing into a viable production-line status.

In the above-cited Sedgwick article, it is pointed out that there isneed to operate at as high a temperature as possible in order to bothactivate the implanted ions and relieve several types of point defects.Applicant is of the opinion that much of the high temperature work hasbeen adequate in regard to temperatures, but has involved scanning laserbeams which heat in small localized areas and develop strains, slippage,ripples and other damage.

A further major factor relating to the viability of rapid annealing iswafer contamination, which is discussed in (for example) the Burggraafarticle (pp. 70 and 71). To prevent contamination, it is important torapidly heat the wafer to 800°-1100° C. (or higher) without touching itor contaminating it in any way. Thus, for example, use of a preheatedplate at high temperatures is distinctly undesirable, for reasonsincluding the fact that material from the plate would enter the wafersin the indicated temperature range.

Other very important factors relating to the question of whether or notrapid annealing apparatus achieves widespread production-line use arethe cost of the apparatus and the cost and difficulty of operating andmantaining it. Efficiency, simplicity, relative compactness, ruggedness,ease of maintenance, etc., are of major importance here as in otherproduction-line operations. And, of course, speed of operation--as wellas versatility and accuracy (for example, accurate temperaturecontrol)--are paramount considerations.

Among the myriad attempts to achieve uniformity of temperature in rapidannealing and other processes, there frequently occur two approaches.One is to transmit the radiant energy through diffusers, for example,quartz sheets or housings that have been sand-blasted or otherwisetreated so as to diffuse light. The other approach, which is often usedwith the first, is to employ susceptors which engage the wafers and aidin heat distribution. Both of these approaches are not desired, and theneed therefor is eliminated by the present method and apparatus. Onereason the approaches are not desired is that they drastically increasethe time required to heat and cool the wafers, thus increasing cycletime and wasting enormous amounts of power.

DEFINITIONS OF CERTAIN TERMS, ESPECIALLY RELATIVE TO WAFER HEATING

There are essentially three methods of heating a semiconductor wafer:

(a) Adiabatic--where the energy is provided by a pulse energy source(such as a laser, ion beam, electron beam) for a very short duration of10-100×10⁻⁹ seconds. This high intensity, short duration energy meltsthe surface of the semiconductor, to a depth of about one to twomicrons.

(b) Thermal flux--where energy is provided for 5×10⁻⁶ to 2×10⁻² seconds.Thermal flux heating creates a substantial temperature gradientextending much more than two microns below the surface of the wafer, butdoes not cause anything approaching uniform heating throughout thethickness of the wafer.

(c) Isothermal--where energy is applied for 1-100 seconds so as to causethe temperature of the wafer to be substantially uniform throughout itsthickness at any given region.

Reference is made to FIG. 8 of the present application for hypotheticalillustrations of isothermal, thermal flux, and adiabatic heating. Thesecurves are not completely to scale. The flat region at the upper end ofthe adiabatic curve is at the melting point of silicon, 1410° C., andresults from the latent heat of fusion required to melt the up to twomicron upper layer of the wafer.

The word "longitudinal" denotes, in the specification and claims, thedirection that extends between lamps and workpiece.

SUMMARY OF THE INVENTION

The present invention provides practical, economical and efficientapparatus and methods for achieving rapid heating of semiconductorwafers by thermal radiation in the visible and infrared regions of thespectrum. Of great importance is the present optical coupling of theradiant source (tungsten-halogen lamps, xenon, arc, krypton arc, mercuryarc, electrodeless radio frequency discharge source, etc.) to the waferbeing treated. The present coupling is such that the intensity ofradiation in the target plane, in which the wafer surface is disposed,is substantially uniform, thus preventing significant temperaturegradients across the wafer. The uniformity is achieved without arequirement for any diffusers or susceptors.

In accordance with one of the aspects of the invention, an integratinglight pipe is employed in combination with a radiant source disposedwithin the pipe, to couple the radiant source with the semiconductorwafer. In the highly preferred form, the integrating light pipe is areflective integrating kaleidoscope containing the radiant source, andthe combination achieves substantially uniform radiant flux at thetarget plane in a high-speed, efficient, economical, noncontaminating,and commercial manner.

In accordance with another aspect of the invention, an extension of theintegrating light pipe is provided on the side of the water remote fromthe radiant source, and performs the functions of reflecting uniformlyback to the wafer those substantial amounts of radiant energy which havepassed through the wafer or around it, and radiated from it.

In a further important embodiment, the same or different radiant sourcesare provided in the extension of the kaleidoscope. In all cases, thereis substantial uniformity of thermal radiation (both direct andreflected) on both sides of the semiconductor wafer.

No scanning lasers are required, but use of a nonscanning laser as oneradiant source is contemplated, this being a large laser combined withan integrator which distributes the laser beam uniformly over the wafersurface.

There is further described a system for effecting substantiallyautomatic heating of wafers in controlled environments for purposes ofannealing, and for other purposes.

The invention also provides a combination of uniform isothermal heatingand uniform thermal flux heating. Thus, isothermal heating is providedby a continuous wave (CW) radiant source located in the optical cavity.Power is controlled to the lamps in order to provide a temperature riserate of about 200° to about 500° C. (for more) per second. When thewafer has reached a predetermined temperature in the range of about800°-1100° C. for silicon, a second radiant source, namely a high-powerpulsed lamp, is energized to quickly elevate the surface temperature ofthe silicon wafer to 1200°-1400° C. (or higher) and thus anneal thesurface and remove defects.

The method described in the preceding paragraph achieves rapid waferheating and annealing without any substantial touching of the wafer, andwithout danger of contamination thereof.

The rapid heating, and uniform optical coupling, result from placementof multiple (or few) quartz halogen lamps and multiple (or few) pulsedlamps in the same integrating optical cavity in order to achievecombined isothermal and thermal flux heating of the semiconductormaterial. The combined heating method, by which the wafer temperature isinitially raised to, preferably, 800°14 1100° C. (for silicon) beforethermal flux heating is effected to raise the surface temperature to,preferably, 1200°-1400° C., significantly reduces the internal stressesresulting from the very rapid annealing. The very rapid annealing,created by the described method, achieves solid phase epitaxial regrowthwith minimum dopant diffusion.

Other important aspects of the invention relate to lamp arrangements,cooling, and temperature control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is isometric external view of the integrating kaleidoscope,portions of the wall being broken away;

FIG. 1a shows prior art;

FIG. 2 is a vertical sectional view on line 2--2 of FIG. 1;

FIG. 2a shows prior art;

FIG. 3 is a horizontal sectional view on line 3--3 of FIG. 2;

FIG. 4 is a vertical sectional view showing a second embodiment of thepresent apparatus, the section being taken in a plane perpendicular tothat of FIG. 2 (which shows the first embodiment), so that the lamps inFIG. 4 are shown in section and not side elevation;

FIG. 5 corresponds to FIG. 4 but shows a much lesser number of lamps atthe bottom of the apparatus;

FIG. 6 corresponds to FIG. 4 but shows a lower aspect ratio at thebottom;

FIG. 7 corresponds to FIG. 3 but shows--in reduced scale--a larger, andotherwise modified, apparatus;

FIG. 8 is a graph showing temperature-depth relationships forisothermal, thermal flux and adiabatic heating;

FIG. 9 is a graph illustrating typical implanted ion density atdifferent depths, both as-implanted and after different types ofannealing;

FIG. 10 is a graph showing a relationship of temperature to time for thefirst method embodiment;

FIG. 11 corresponds to FIG. 10 but relates to the second embodiment ofthe method;

FIG. 12 is a schematic view of an automatic system for effecting rapidheating of semiconductor wafers in a production line;

FIG. 13 is a horizontal sectional view corresponding to FIG. 3 butshowing the form in which the cross-sectional shape of the opticalcavity is a regular hexagon;

FIG. 14 is a horizontal sectional view corresponding to FIG. 3 butshowing the form in which the cross-sectional shape of the opticalcavity is an equilateral triangle; and

FIG. 15 is a horizontal sectional view corresponding to FIG. 3, butshowing the form in which the cross-sectional shape of the opticalcavity is a rectangle.

The curves of FIGS. 8 through 11, inclusive, are theoretical only andare not presented as representing actual laboratory data. In FIG. 9, thecurves relate to prior art.

DETAILED DESCRIPTION OF APPARATUS

It has for decades been known, in arts including the heating ofworkpieces, to direct light or other radiant thermal energy nonuniformlyinto the entrances of integrating light pipes, the light pipes operatingto render the light relatively uniform by the time the exit ends arereached. One type of such light pipes employs, wholly or partly,diffusely reflective surfaces on the interior thereof.

A second type of integrating light pipes, which has been used in theprior-art as stated above, is termed a "kaleidoscope". This second typeis greatly preferred for reasons including its ability to achieveuniform temperatures, and its much greater efficiency. It has highlyreflective and (at least primarily) nondiffusing internal walls arrangedin predetermined cross-sectional shapes. These shapes include thesquare, the regular hexagon, the equilateral triangle, and therectangle. All of such cross-sectional shapes will "nest", or fittogether (without leaving voids), with cross-sectional shapesrespectively identical thereto. For example, several equilateraltriangles of identical size will nest with each other, as will severalsquares, etc. Reference is made to the first two pages of an articleentitled "The Use of a Kaleidoscope to Obtain Uniform Flux Over a LargeArea in a Solar or Arc Imaging Furnace", by M. M. Chen, J. B.Berkowitz-Mattuck, and P. E. Glaser (Applied Optics, March, 1963, Vol.2, No. 3, pp. 265-271). Said first two pages (pp. 265 and 266 of AppliedOptics) are hereby incorporated by reference herein.

As used in the present specification and claims, and except wherespecifically stated otherwise, the word "kaleidoscope" denotes such areflective, integrating light pipe, described in the precedingparagraph, adaptive to achieve relative uniformity of radiant flux at atarget plane by covering such target plane as the result of multiplereflections of the incident radiant energy by The planar and (at leastprimarily) nondiffusing interior walls of the light pipe. The expression"substantially nesting cross-sectional shape" is used, in some of theappended claims, to denote cross-sectional shapes that will nest withother identical shapes and sizes, as stated in the preceding paragraph.The word "substantially" is intended to comprehend cross-sections wherethe angles are not perfect but are still sufficiently close to perfectto create much uniformity. It is, however, pointed out that not onlycross-sectional shape but aspect ratio and number of lamps areimportant, these factors being discussed subsequently in thisspecification.

The following quoted material constitutes portions of saidabove-referenced pages 265 and 266 of the above-cited Applied Opticsarticle. (Titles, headings, footnotes and "Appendix A" of such pages areomitted, as are some paragraphs. The expressions "FIG. 1" and "FIG. 2"of such pages have been changed, respectively, to "FIG. 1a" and "FIG.2a", such FIGS. 1a and 2a appearing in the drawings hereof.)

"The use of properly designed light pipes to redistribute the energy ofa solar furnace or an arc imaging furnace is discussed. Compared toalternate schemes of obtaining uniform irradiation over a large area,the light pipe has the advantage of good uniformity without a seriousloss of efficiency. Theoretical analyses concerning the principle ofoperation, as well as formulas for estimating the flux uniformity andreflection losses, are discussed. The results also indicate that theonly suitable cross sections are the square, triangular, hexagonal, andrectangular. Other cross sections, including the circular, are notsatisfactory unless used with diffusely reflecting surfaces.

"The termal flux at the focal spot of a typical solar furnace or carbonarc is of the order of 250 cal/cm² -sec, concentrated within a circulararea approximately 0.6 cm in diameter. For many applications a smallerflux is required, spread uniformly over a larger area. The simpleexpedient of placing the sample in an off-focus position is not entirelysatisfactory, because shadows from sample holder and supports limit fluxuniformity more and more seriously with increasing distance from thefocal plane. A superior technique that has been used successfully inthis laboratory is to interpose a light pipe, or mirrored box, betweenthe focal plane and the sample plane. This device collects the energyfrom the focal spot, reflects it a large number of times, like akaleidoscope, and redistributes it uniformly over an area equal to thecross section of the light pipe. In the following sections, we describethe theory and application of several light pipes as flux redistributorsin imaging furnaces.

"The light pipe that has been used most frequently in our laboratory isshown in FIG. 1a. It is essentially a short pipe, 6 cm in length, with a2×2 cm square cross section. The four inside surfaces arechromium-plated to a highly reflective mirror finish. When used in thesolar furnace, the pipe is placed on the side of the focal point awayfrom the collector mirror in such a way that the front surface of thelight pipe coincides with the focal plane, and the focal spot is locatedat the center of the square opening. The sample is placed at the rearsurface of the light pipe. This arrangement ensures that all of theradiation collected by the furnace also enters the light pipe and isused to irradiate the sample area. The only energy losses will be due toadsorption at the mirrored planes.

"In FIG. 2a, F denotes the focal spot of the solar furnace. If the lightpipe were removed, energy would diverge from the focal point andilluminate an area B. The effect of the light pipe is to subdivide thearea B into any array of squares and to re-sum the fragments over thearea A=a², where a is a side of the cross section of the light pipe. Inother words, the squares in area B are superimposed on each other at A.If an arbitrary point (x,y) is selected in the A plane, then all of theimages of this point in the B plane are easily found by reflection. Theflux intensity at (x,y) is simply the sum of intensities that would beobserved at the image points, in the absence of the light pipe. Sinceeach individual square of B contributes only a small portion of thetotal irradiance at A, nonuniformities in the flux that might haveexisted in individual squares cannot contribute significantnonuniformity to the exposed area A.

"While our experience has been confined almost entirely to square lightpipes, other cross sections are obviously possible, and may be desirablefor particular applications.

"In general, a straight light pipe, or one with constant cross-sectionalarea throughout its length, can be used to achieve uniform illuminationover a sample area if, and only if, it can completely cover the plane bymultiple reflections with respect to the straight sides. Thus, theuseful cross sections appear to be the equilateral triangle, the square,the regular hexagon, and the rectangle. Such light pipes wouldeffectively subdivide the B plane (FIG. 2a) into corresponding polygons,and the net intensity at any point of the A plane of the light pipecould be found by reflection as described above."

By the present invention, applicant makes use of an integrating lightpipe, very preferably a kaleidoscope, in novel ways that achieve majorresults relative to the treatment of large-diameter semiconductorwafers. In accordance with one aspect of the invention, applicant doesnot funnel radiant flux into the light pipe from the outside but insteadplaces sources of incoherent radiation in the pipe itself, verypreferably near one end thereof, and such end is closed and internallyhigh reflective. By placing the incoherent radiant sources on theinside, applicant causes the radiation to travel out in all directionsfor eventual reflection to a target plane located at a distance spacedfrom the radiant sources. The described aspect of the invention causesmarkedly increased compactness, efficiency and economy of the apparatusfor a given degree of temperature uniformity at the target plane.

In accordance with another aspect of the invention, the semiconductorwafer is placed at any desired point along the length of the light pipe,at a distance sufficiently far from the radiant sources to achievesubstantial uniformity of radiant flux across the plane, that is to sayover the entire surface of the wafer. Great advantages--such as, forexample, elimination of edge effects and achievement of highefficiency--are obtained when the wafer is not located at or adjacentany exit end but is instead disposed in a substantially fully-enclosedoptical cavity all the walls of which are reflecting. That is to say,both end walls cooperate with the kaleidoscope sidewalls to form asubstantially fully-enclosed optical cavity having a vast capability ofuniformly heating a semiconductor wafer.

The diameter of the light pipe, namely, the diameter of the elongatedcavity, may be increased to the extent desired, as required by thediameters of the semiconductor wafer or wafers being treated. Thus, forexample, wafers four inches in diameter may be treated in kaleidoscopeshaving internal diameters of four and one-half inches. On the otherhand, wafers six inches in diameter may be treated in kaleidoscopeshaving internal diameters of, preferably, about seven inches. When morethan one wafer is treated at once, the cavity size is increasedaccordingly. These and subsequent examples are given by way ofillustration only, not limitation.

The first embodiment is illustrated by FIGS. 1-3 and 10. This embodimentis preferred at least for annealing semiconductor wafers having lowerdensity implants, namely implant densities up to 5×10¹⁵ ions/cm². Thesecond embodiment, described subsequently relative to FIGS. 4 and 11, ispresently preferred at least for annealing wafers having higher densityimplants, namely those semiconductor wafers having implant densitiesgreater than 1×10¹⁶ ions/cm².

Referring to FIGS. 1-3, an integrating light pipe of the kaleidoscopetype is shown at 10. In the illustrated form, the light pipe is formedby four metal sidewalls 11 (for example, aluminum) which are securedtogether to form a perfect square (FIG. 3). The end of the pipe in whicha radiant source is disposed, namely the upper end as viewed in FIGS. 1and 2, is closed by a metal end wall 12 (for example, aluminum) whichlies in a plane perpendicular to the longitudinal axis of the lightpipe.

The internal surfaces of walls 11 and 12 are made hightly reflective ofthe type of radiation generated by the radiant source employed. At leastrelative to the preferred radiation source specified below, the internalwall surfaces are provided with nondiffusing coatings 13 of gold thathas been evaporated onto polished surfaces.

As shown in FIGS. 1 and 2, the radiant source 14 is disposed within theoptical cavity 16 defined by walls 11 and 12, and for maximizedefficiency and compactness is located closely adjacent end 12. Thepreferred radiant source for continuous wave (CW) operation is an arrayor bank of relatively closely-packed lamps 17 which blanket,substantially entirely, the end of the cavity 16 and which radiate lightin all directions. The preferred embodiment comprises a plurality oflayers of parallel tubular lamps, which are offset row-to-row so as tomaximize transmission of light from the upper layer down thekaleidoscope. The preferred lamps are quartz halogen, but other types ofCW lamps, such as argon, xenon, mercury, etc., may be used. The lampsare disposed in planes perpendicular to the longitudinal axis of thekaleidoscope.

For performing some methods, the number of lamps may be reduced greatly,as described below relative to FIG. 5, for example.

The workpiece, in this case a semiconductor wafer, to be treated isnumbered 18, being disposed in a target plane (or target area) that isperpendicular to the longitudinal axis of kaleidoscope 10. Theillustrated wafer is just below the lower edges 19 of kaleidoscope walls11.

As indicated previously, an extremely important and unique feature ofthe system is its ability to generate (practically, efficiently,economically, etc.) the substantially uniform radiant flux intensity atthe wafer surface. This is accomplished by multiple reflections of theradiation (visible and infrared) emitted by the lamps. The radiationpreferably emanates from the lamps in all directions. That radiationwhich emanates vertically-downwardly strikes the wafer surface directly,without being reflected. Other radiation reflects back and forth betweenthe sidewalls 11 and then strikes the wafer surface. Additionalradiation reflects off the end wall 12 and then down to the wafersurface, either directly or after reflecting off one or more walls 11.

Some of the radiation, namely, that portion of the radiation which is inthe planes of the lamp filaments, does not reach the wafer at all. Suchradiation, however, performs the beneficial and energy-conservingfunction of aiding in heating of the filaments.

The wafer 18 is supported, in the illustrated form, by a ring 21 formedof quartz and having a diameter substantially larger than that of thewafer, the excess diameter being to prevent edge effects, namely, edgetemperatures that are not the same as the temperature of the rest of thewafer. A handle 22, also formed of quartz, is connected to ring 21 andpasses outwardly. Curved support elements 24 formed of quartz areconnected to ring 21 and curve upwardly below wafer 18 for point-contactsupport therewith. In other words, the ends of the elements 24 remotefrom ring 21 are pointed and directed upwardly, to thus minimize contactbetween the wafer and the quartz.

It is possible to not have any cavity region below the wafer 18, butinstead to place the wafer in or near the same plane as the lower edges19 of sidewalls 11 of the kaleidoscope, and with no additional wallstherebeneath. In such a form, baffles, reflectors etc., are providedaround the wafer and in relatively close adjacency thereto but withouttouching. Although such a form works for some applications, in a certaindegree, the form next described is highly preferred.

A second integrating light pipe, numbered 29, is mounted axiallyadjacent the first kaleidoscope 10. Light pipe 29 is, very preferably, akaleidoscope constructed, and cross-sectionally sized and shaped,substantially identical to kaleidoscope 10, and rotationally and axiallyaligned therewith. Thus, the second kaleidoscope 29 cooperates with thefirst kaleidoscope 10 to form a single, longer, kaleidoscope having thewafer 18 at an intermediate region. Kaleidoscope 29 has sidewalls 31 andan end wall 32 which correspond, respectively, to sidewalls 11 and endwall 12, being the mirror images thereof. However, end wall 32 is closerto wafer 18 than is end wall 12, and still produces highly satisfactoryresults. Walls 31 and 32 have nondiffusely-reflective coatings 33thereon.

When wafer 18 is relatively cold, shortly after energization of radiantsource 14, much of the radiant energy is transmitted through the waferas stated previously. Furthermore, much of the energy passes around theedge of the wafer, especially through the corner regions shown in FIG.3. After the wafer becomes hot, it is a black-body radiator thatradiates energy downwardly into the portion of the cavity below wafer18. The large amounts of energy which pass through and around the wafer,and which are radiated from the wafer after it becomes hot, arereflected by the coatings 33 on walls 31 and 32 until, after a number ofreflections, the energy passes upwardly to the target plane and strikesthe bottom surface of wafer 18 in substantially uniform manner. Thus,wafer 18 is being rapidly heated from both sides even though, in theillustrated embodiment, only one radiant source 14 is employed.

It is a major feature of the invention that there are no edge effects;no substantial temperature difference between the edge regions of thewafer and the central regions thereof. The heating is substantiallyuniform across the entire wafer. Also, there is no contamination of anyconsequence, the only actual contact with the wafer being at the sharppoints of the support elements formed of quartz. As described below, acontrolled atmosphere, or a vacuum if desired, is maintained around thewafer to prevent oxidation thereof and achieve other desired results.

Full symmetry may be achieved by providing a second array of lamps 17,or other radiant thermal source 14, adjacent a bottom wall but at thesame distance from wafer 18 as is the first array 14 therefrom. In sucha form, the wafer 18 is radiated uniformly from both sides. In eachinstance, thermal flux from each radiant source ricochets between thereflective coatings a sufficent number of times to cause the flux to beuniform at the target plane, and, furthermore, energy that passesthrough and around the wafer ricochets a sufficent number of times to beuniform by the time it reflects back to the target plane.

DETAILED DESCRIPTION OF THE SECOND EMBODIMENT OF APPARATUS (FIGS. 4 AND11)

FIGS. 4 and 11 show an embodiment where different types of radiantthermal sources are employed, one source being CW and the other pulsedor flash. Thus, the present embodiment is particularly adapted to beemployed in the method by which isothermal and thermal flux heating arecombined as indicated above, and as described in detail subsequently.

In FIG. 4, the radiant source 14 is shown as being at the bottom insteadof at the top as illustrated in FIG. 1. The source 14 is shown intransverse section in FIG. 4, schematically, and it is to be understoodthat the arrangement of the lamps in source 14 at the bottom of FIG. 4is identical to that described above relative to the FIGS. 1 and 2.

The upper integrating light pipe, very preferably the kaleidoscope asdescribed, is indicated at 10a; the sidewalls thereof at 11a; thenondiffusing reflective coatings at 13a; and the end wall at 12a. Thelower light pipe (kaleidoscope) is identical to the one describedrelative to the previous embodiment, but is inverted. Thus, the samereference numerals 10, etc., are used.

The radiant source at the upper end of kaleidoscope 10a is numbered 46.It is a pulsed or flash source, shown as being three flash tubes 47disposed in parallel spaced relationship relative to each other in aplane perpendicular to the axis of the kaleidoscope. As an example, eachof the three flash tubes 47 is a linear air-cooled flash lamp adapted toprovide a 700 joules discharge in 50 to 100 microseconds. Because of thecharacteristics of the flash tubes, it is preferred that thenondiffusing reflective coatings 13a be aluminum instead of the goldpreferably used relative to the quartz halogen CW lamps.

The flash tubes 47 may be, for example, xenon flash tubes and arestrobed to achieve high-power and short-duration flashes. Because of theinternal reflections in the kaleidoscope 10a, the large-area wafer 18 isheated uniformly by energy from the pulse source 46, it being understoodthat the flash tubes 47 are strobed simultaneously relative to eachother.

In one (unshown) embodiment of the apparatus, the flash tubes 47 areomitted and a fly's-eye integrating lens is mounted centrally in upperwall 12a coaxially of the kaleidoscope 10a. A large neodymium-YAG orneodymium-glass laser is provided above the kaleidoscope 10a, with itsbeam directed at the fly's-eye integrator in wall 12a. The laser is thenpulsed to provide, simultaneously and without scanning, radiant energyover the entire upper surface of wafer 18. Such pulse heating by thelaser is rendered effective because of the uniform heating actionprovided by the CW source 14.

DESCRIPTION OF THE EMBODIMENTS OF FIGS. 5 AND 6, OF ASPECT RATIOS ASCORRELATED TO LAMP NUMBERS AND CHARACTERISTICS, AND OF CERTAIN OTHERFACTORS

Particular reference is made to the embodiments of FIGS. 5 and 6, whichwill now be described, but it is to be understood that statements madebelow relating to aspect ratios versus lamp numbers and characteristicsapply to all embodiments of the invention.

Within certain limits, the greater the number and uniformity of thelamps, the lower the aspect ratio can be and still achieve the desireddegree of uniformity of thermal flux across the entire workpiece. The"aspect ratio" is the distance of the lamps from the workpiece dividedby the diameter of the optical cavity.

When there are many and uniformly-spaced lamps, the radiation therefromdoes not have to reflect so many times in order to achieve the desireduniformity of thermal flux at the plane of the workpiece. When, on theother hand, there are but few lamps, more internal reflections areneeded to achieve the desired uniformity of heating. Thus, the aspectratio in the first-mentioned case is caused to be lower than in thesecond-mentioned case.

Other factors also have bearings on the desired aspect ratio. Forexample, causing the internal surfaces of the end walls of the opticalcavity to be diffusely reflective instead of nondiffusely reflective canreduce the aspect ratio (however, such non-diffuse reflectors increaseend-wall heating). Also, it is pointed out that where one of two alignedcavities has no substantial lamps therein, as in the illustrated exampleof FIGS. 1 and 2 (bottom end), the distance from the bottom end wall tothe workpiece 18 can be very short. This is because radiation comes fromthe upper cavity (FIGS. 1 and 2), makes one pass downwardly through thelower cavity, reflects off reflector 33 of bottom end wall 32, and thenpasses upwardly to wafer 18--with numerous reflections off thesidewalls. The effective length of the lower cavity is thus doubled,permitting the lower cavity to be short.

As a general rule, the aspect ratio in a particular cavity should be atleast about one when there are many uniformly-spaced lamps in suchcavity. The aspect ratio should be substantially more than one, forexample, two, when there are only few (or one) lamps in the cavity.

As stated above, aspect ratio is distance of lamps from the workpiece,divided by cavity "diameter". For kaleidoscopes having sides of equallength, viewed in cross-section, the "diameter" referred to above issubstantially the diameter of a circle inscribed within the walls of thekaleidoscope. Thus, for example, for a kaleidoscope that is square incross-section, such diameter is equal to the length of each side.

Relative to kaleidoscopes rectangular in cross-section, the desiredaspect ratio is determined empirically by reference to thecharacteristics of kaleidoscopes square in cross-section. When the sidesof the rectangle (viewed in section) are relatively equal in length, theaspect ratio is generally the same as or similar to that of asquare-sectioned kaleidoscope. It is pointed out that the rectangularkaleidoscope should not be very long and narrow in section--havesidewalls the lengths of which are drastically different from thelengths of the other two walls--because many of the benefits describedin this specification are lost. As an extreme example, when thesidewalls have lengths (in section) many times the lengths of theremaining two walls, the apparatus acts more like only two parallelreflectors, there being undesirably low reflections from the other twowalls.

Except as specifically set forth, FIG. 5 corresponds to FIG. 4 and hasbeen numbered correspondingly. In the embodiment of FIG. 5, the numerousCW lamps 17 of FIG. 4 are replaced by only a few CW lamps 17. Forexample, three such CW lamps are shown. The three lamps 17 are equallyspaced across the cavity 16.

In FIG. 5, the lamps at both ends of the apparatus are few in number.There is, however, still sufficient uniformity of heat flux, at theplane of the workpiece, to satisfy the uniformity requirements of manysemiconductor processes.

To achieve such uniformity, with relatively few lamps, the aspect ratiois made larger than 1, and preferably about 2. Thus, each set of lampsis located at a distance from workpiece 18 that is about twice thediameter of the cavity 16.

Referring next to the embodiment of FIG. 6, this is also identical tothat of FIG. 4, except as specifically stated. In FIG. 7, the densearray of CW lamps 17 is located much closer to wafer 18 than is the caserelative to FIG. 4. Stated more definitely, the aspect ratio in FIG. 7,relative to lamps 17, is about 1, the lamps 17 being spaced from thewafer a distance about equal to the diameter of the cavity. Because ofthe changes, certain reference numerals at the bottom of FIG. 6 arefollowed by the letter "b".

The radiation from the tightly-packed lamps 17 is not uniform, as mightbe thought. For example, the central lamps 17 in FIG. 6 are (assumingthe same current) hotter than the outer lamps. This is especially truebecause the outer lamps 17 are near relatively cold walls.

Despite such (and other) disuniformity of thermal flux radiated fromlamps 17, there is much less disuniformity than is the case relative tothe few CW lamps 17 of FIG. 5, or relative to the few flash tubes 47.Accordingly, the aspect ratio relative to CW lamps 17 can be less in theembodiment of FIG. 6 than in that of FIG. 5.

The present apparatus and methods are extremely versatile in theirability to do many things needed by manufacturers in makingsemiconductor wafers, large scale integrated circuits, etc. This isbecause manufactures can now effect rapid and efficient uniform heatingto substantially any temperature desired, in any desired atmosphere, andwithout substantial contamination. In some cases the temperatures willbe high, at or near the melting points of the workpieces. In other casesthe temperatures will be low. Furthermore, the heating may be--asdesired by the manufacturer--isothermal, thermal flux or adiabatic, orcertain combinations thereof.

When a large amount of heat is required, and/or when it is desired thatthe apparatus be compact, a bank or array of numerous lamps is used asdescribed relative to FIGS. 1 and 2 and relative to the bottom portionsof FIGS. 4 and 6--the latter FIG. showing a low aspect-ratio apparatusthat is consequently compact. When the required heat is low, the numberof lamps is reduced, as shown in FIG. 5, but the aspect ratio is causedto be more than one in order to achieve the desired degree ofuniformity.

In all cases where the manufacturer desires a very high degree ofthermal flux uniformity across the wafer or other workpiece, the aspectratio and the number of lamps are caused to be sufficiently large--andthe degree of perfection of the shape of the kaleidoscope is caused tobe sufficiently high--that the thermal flux uniformity is as desired.The preferred range of such thus-achieved thermal flux uniformity acrossthe workpiece is plus or minus a few percent, more preferably plus orminus 2%, but uniformities closer to plus or minus 1% are practicallyand efficiently achievable by the present apparatus and method.

As previously emphasized, the kaleidoscope with nondiffusely-reflectivewalls is greatly preferred over other types of light pipes. The onlytime a diffuse wall is sometimes desired is at the end or ends, in orderto reduce the aspect ratio, and this is at the expense of power losscaused by increased heating of the end walls.

Kaleidoscopes having diffusely-reflective sidewalls can be made to workto a degree, especially where the diffusion is partial (walls quitesmooth instead of rough).

Preferably, the kaleidoscope is substantially uniform in cross-sectionalarea throughout its length. Kaleidoscopes that converge steeply from thelight source toward the workpiece tend to "trap" a large percentage ofthe light, so that it never reaches the workpiece. On the other hand,kaleidoscopes that diverge steeply from the light source toward theworkpiece markedly reduce the number of re-reflections, and consequentlythe uniformity. Further, such divergent configurations leave but littleroom for the light sources.

The preferred cross-section of the kaleidoscope is square, as shown inthe present drawings. Hexagonal kaleidoscopes can increase manufacturingdifficulty, while triangular ones reduce effective work area (with noedge effects) for disc-shaped wafers, and also limit the lamp area.

APPARATUS OF FIG. 7

FIG. 7 corresponds--except as stated below--to FIG. 3, and except asspecifically stated, the embodiment of FIG. 7 corresponds to that ofFIGS. 1-3. However, the statements made relative to FIG. 7 apply notonly to the embodiment of FIGS. 1-3 but also to other embodiments (forexample, that of FIG. 4).

The size of the present apparatus may be increased markedly, so as topermit annealing or other process steps to be performed simultaneouslyrelative to two or more wafers 18. Thus, for example, two wafers 18 maybe treated in an apparatus (not shown) of rectangular section.

In FIG. 7, eight wafers are shown as supported by rings 21 about a largecavity of square cross-section. Such cavity has the same aspect ratio asshown and described relative to other embodiments. Thus, since thecavity of FIG. 7 is relatively large in section, the length of theoptical cavity is proportionately larger.

The lamps must be greatly increased in number, power, etc., in thepresent embodiment where a plurality or workpieces 18 are simultaneouslyannealed or otherwise treated.

It is greatly preferred that the walls 11c of the optical cavity of FIG.7 have nondiffusely-reflective coatings, as described above and for thereasons previously stated. However, in FIG. 7 the internal surfaces "d"are diffusely reflective (as by being lightly sand-blasted, chemicallytreated, or coated).

The adverse effects of the diffusing surfaces "d" of FIG. 7 (as comparedto the nondiffusely reflective gold or other nondiffusely-reflectivemirror surfaces described above) are lessened since there is no wafer 18in the center of the cavity. Diffuse reflectors such as indicated at "d"tend to increase the amount of radiant energy at the center of thecavity, at the expense of the peripheral cavity regions.

DETAILED DESCRIPTION OF METHODS

In accordance with a first method, a CW radiant source is employed incombination with an integrating light pipe to effect rapid and uniformheating of a semiconductor device, component or material to such atemperature, and for such a time period, as to achieve the desiredeffect. The rate of heating may be controlled as desired, in aprogrammed manner. The heating is isothermal, as defined under theDefinitions portion at the beginning of the specification and as shownin FIG. 8. The light pipe is, in the greatly preferred form, thedescribed kaleidoscope.

Where the desired effect is rapid annealing of an ion implantedsemiconductor wafer, the method comprises supplying a large amount ofpower to the CW source, then drastically reducing the power as soon as adesired "holding" temperature is achieved, and then substantiallyreducing or turning off the power to permit cooling of the wafer. Thepower may be reduced in a programmed manner to fully control the coolingcycle, it being understood that cooling rate is far less rapid in theoptical cavity than it would be in open space. Preferably, thetemperature rise rate is (for silicon) in the range of 200°-500° C. persecond. The holding temperature is, for silicon, preferably about1000°-1200° C. and continues for several seconds, following which thereis a cooling period of about ten or fifteen seconds. Exemplary time andtemperature relationships are illustrated in FIG. 10 which shows therelatively steep temperature rise at the left, the flat holding periodat the top, and the cooling period at the right. The curve relates tosilicon, which has a melting point of approximately 1410° C.

As stated previously, the above-described first method is presentlypreferred at least for lower density dopant implants. There will next bedescribed a second method, which is presently preferred for the higherdensity dopant implants.

The second method of rapid annealing a dopant implanted semiconductorwafer comprises effecting uniform isothermal heating of such a wafer toa predetermined temperature well below the melting point thereof,thereafter immediately effecting thermal flux heating of the upper(assuming that the upper side is the one that has been dopant implanted)surface region of the wafer, and thereafter permitting the wafer tocool. Preferably the thermal flux heating (as that term is defined underDefinitions at the beginning of this specification) approaches themelting point of the semiconductor material but does not reach the same,as shown by the spike at the central region of FIG. 11 and in relationto the 1410° C. melting point of silicon.

Stated more specifically, the second method comprises effectingisothermal heating of the dopant implanted wafer by a CW radiant source,preferably an array of quartz halogen lamps, disposed within the opticalcavity formed by the light pipe (preferably, the kaleidoscope). Power tothe CW lamps is controlled in order to provide the temperature rise rateof 200°-500° C. (or more) per second. When the silicon wafer has reacheda programmed temperature of 800°-1100°C., a second, high-power, pulsedlamp array is energized to quickly elevate the temperature of thedopant-implanted surface of the wafer to 1200°-1400° C., or higher, thusannealing the surface region and removing defects.

The method of combined heating provides rapid, efficient, and effectiveheating of the wafer without touching it or contaminating it in any way,there being no need for (for example) a hot plate. The multiple quartzhalogen lamps and the multiple high-power (pulsed) lamps are provided inthe same cavity in order to achieve combined isothermal-thermal fluxheating of the semiconductor material. There is no need, in this or anyembodiment, for a susceptor or diffuser to improve heating uniformity.

Pulse duration of the pulsed lamp array can be from five to one thousandmicroseconds. Absorbed thermal flux energy on the dopant-implantedsurface of the semiconductor material can range from 0.5 J/cm² for a 5microsecond pulse to as much as 10 J/cm² for a 1,000 microsecond pulse.

It is emphasized that, in the described second method and as shown inFIG. 11, the isothermal heating is preferably to a lower temperaturethan is the case when only isothermal heating (no pulse) is employed, asshown in FIG. 10. The spiking of the surface temperature to near themelting point of the semiconductor material greatly increases theannealing speed (much more so than would be the case if the temperaturevs. anneal speed relationship were linear). Thus, a lower isothermaltemperature can be used.

As an example, let it be assumed that the isothermal heating is employedto raise the temperature of the entire wafer uniformly up to about 1100°C. After a few seconds, the pulse source is energized to create thespike (FIG. 11) and raise the temperature of only the upper surfaceregion to a peak near but not at the melting temperature of theparticular semiconductor material (silicon, in the showing of FIG. 11).The pulse is sufficiently short to heat and anneal the region at leastas deep as the depth (bottom) of the dopant implant layer, but theduration of the pulse is sufficiently short (especially after theisothermal heating) that slippage of silicon planes is minimized and,furthermore, overall heating of the body of the wafer is extremelysmall. Relative to the latter factor, the temperature of the entirewafer may only increase a few degrees, from the 1100° C. stated in thespecific example, because of the shortness of the pulse which providesthe thermal flux heating.

It is emphasized that for other semiconductor materials, such as galliumarsenide, the temperatures and/or times are changed. There is a majorproblem in the prior art relative to gallium arsenide, because ofvaporization that occurs during slow (furnace) annealing. For galliumarsenide, the presently described second method may be employed toisothermally heat the wafer to a relatively low temperature at which nosubstantial vaporization occurs. Then, the pulsed lamps are employed forthermal flux heating to achieve (in combination with the isothermalheating) the desired annealing. Stated more definitely, the galliumarsenide semiconductor wafer is quick annealed, by the second method, byheating it isothermally to a temperature in the range of about 500°-600°C., and then spiking the surface temperature to about 950°-1000° C.

The combination of isothermal and thermal flux heating may be soperformed that melting occurs, that is to say, the spike shown in FIG.11 extends upwardly to 1410° C. (for silicon) and flattens off becauseof the latent heat of fusion. Melting is desired for some processes.However, when the process being performed is annealing, melting is notpreferred. Melting may also be performed, when desired, by thefirst-described method, that of FIG. 10.

It is pointed out that the kaleidoscope and other apparatus describedearlier in this specification may also be employed relative to pulsesources by themselves, in the absence of CW lamps or isothermal heating.The pulse (flash) sources of radiant energy may be such as to provideeither thermal flux heating or adiabatic heating, reference being madeto FIG. 8.

To increase the rate of production, means may be employed to increasewafer cooling speed. Thus, for example, the light pipes may beseparated, and/or gas flow increased, during the cooling period.

FURTHER METHODS RELATING TO CERTAIN MATERIALS

The present apparatus and method uniformly heat silicon (or other)wafers in any controlled atmosphere, and with very accurate computercontrol of temperature, so that a wide variety of different processsteps may be performed. The wafer may be brought to and held at onedesired temperature while one step is performed, then changed to anothertemperature while another step is performed in the same--or adifferent--atmosphere. These can be sequential or simultaneous vapordeposition, annealing, diffusion, and other process steps. New alloysmay be generated cheaply and effectively at the surface of a wafer, toachieve desired results such as reduced use of gold. Large scaleintegrated circuits may be built up using relatively low-cost silicon asthe base material.

For example, the wafer may be heated in the presence of oxygen,nitrogen, or both, to create different types of insulating or dielectriclayers in an integrated circuit.

Also, in the formation of low-reistance silicides, refractory metalssuch as tantalum, tungsten, molybdenum, titanium, etc., may be appliedto the silicon by chemical vapor deposition at one desired temperature,then rapidly diffused or alloyed at another desired temperature. Thesurfaces may be melted, remelted, annealed, etc., as desired.

As previously indicated, silicide formation and annealing may beachieved sequentially or substantially simultaneously. Alloying may beperformed, for example at the wafer surface, at any desiredtemperature--even one as low as 450° C. or lower.

Since no diffusers, susceptors, hot plates, etc., are required ordesired, every step may be performed so fast--and withoutcontamination--that the number of possible and practical process stepsis vast.

DESCRIPTION OF LAMP-COOLING MEANS AND METHOD, AND POWER SOURCE ANDCONTROL ELEMENTS

The upper portions of FIGS. 1 and 2, and the lower portion of FIG. 4,depict the number and type of lamps 17 preferably employed in theexemplary annealing apparatus wherein the wafer 18 has a diameter of sixinches, and the internal diameter of the optical cavity is approximatelyseven inches. Twenty-seven lamps 17 are used, each lamp 17 having arating of 1.5 kilowatts. Thus, the combined kilowatt ratings of thelamps 17 in the array total 40.5 kw.

There will next be described the apparatus for supplying power to thelamps 17 and effectively cooling them, without generating andmaintaining excessive heat in the optical cavity 16 even when theapparatus is employed hour after hour in production. The descriptionrelates to FIGS. 1 and 2, but applies also to many other embodiments.

As shown in FIGS. 1 and 2, each lamp 17 (which is preferably a quartzhalogen lamp) has a length substantially greater than the outer diameterof the optical cavity, so that the terminations 48 at the outer ends ofthe lamps are spaced away from the walls of such cavity. Terminations 48are connected to bus bars 49-52 that are also spaced away from thecavity walls. Three of the bus bars, numbers 49-51, are disposed on oneside of the optical cavity, and each is connected to the terminations 48of nine of the lamps 17. The remaining bus bar, number 52, is providedon the other side of the optical cavity, and connected to all of thetwenty-seven lamps.

A power supply 53, shown in FIG. 2, is suitably connected in delta or Yrelationship to the three bus bars 49-51, and is also connected to theremaining bus bar 52, such lamps thus being supplied with three-phasepower. Power supply 53 is of the SCR type, and preferably of the typewhere the power delivered to the lamps is controlled by a variablevoltage. (One source of such a supply is the Vectrol Division ofWestinghouse Corporation.) The control signal is delivered to powersupply 53 from a computer 54 (FIG. 2) that is, in turn, connected to anoptical pyrometer 56. The pyrometer 56 is directed through an inclinedaperture 57 in a sidewall 11 at the center region of semiconductor wafer18. Elements 53, 54 and 56 are adapted to cause the wafer temperature 18to rise rapidly (in abrupt or programmed manner) to the desired levelfor the isothermal heating, as described above relative to FIGS. 10 and11, thereafter to hold the desired temperature for a desired timeperiod, and thereafter to discontinue (in abrupt or programmed manner)supply of power to the lamps.

Referring next to the cooling of the CW lamps, it is pointed out thatthe filaments of the lamps are entirely within the optical cavity. Thus,for example, each lamp 17 has a filament about 6.2 inches long and isdisposed entirely within cavity 16. Much of the heat generated by thelamps is at the terminations 48, and these are spaced outwardly from thewalls of the cavity as described. The present cooling apparatus andmethod cause a high degree of cooling of the terminations 48 and busbars 49-52, by air flowing on both sides of the bus bars. The apparatusand method also cause sufficient cooling of those portions of lamps 17within optical cavity 16 to prevent overheating of the apparatuswithout, at the same time, cooling the lamp tubes so much that thehalogen vapor deposits thereon and reduces lamp efficiency.

A coolant housing 59 is mounted around the end of the optical cavity inspaced relationship therefrom and from bus bars 49-52. Air or othersuitable coolant is supplied to the housing 59 through a conduit 60, andwithdrawn from the housing through conduit 61. Suitable baffle means,such as vertical baffles 62, divide the coolant housing 49 into an inletchamber 63 and an outlet chamber 64 between which coolant cannot flowexcept along two predetermined paths.

The first such path is a large-area path and it is past the end wall 12of the optical cavity. The second path is into the interior of the endportion of the optical cavity 16, through oversized ports 66 providedone for each of the lamps 17. The ports 66 are preferably cylindricaland concentric with the lamps, so that the walls of the lamps do nottouch walls 11 of the cavity. The lamps, instead of being supported bythe cavity walls, are supported by the buses 49-52 which, in turn, aresupported by insulating brackets 67 connected to the cavity walls.

Thus, air from inlet chamber 63 flows into the upper end of cavity 16along and around each of the lamps 17, then flows through the upperportion of the optical cavity, then flows outwardly into chamber 64 foroutflow via conduits 61. The end portions of the optical cavity areseparated from the cavity portions adjacent wafer 18, by quartz windows68 (and 68a, FIG. 4). Windows 68 need not be, and preferably are not,diffusing, being instead clear and transparent. Thus, air is preventedfrom reaching the wafer 18 and, furthermore, a controlled atmosphere maybe provided on both sides of the wafer 18 as described subsequently.

The combination of the cooling means, the bus and end-termination means,and the windows 68 provides an effective and efficient cooling action.Walls 11 and 12 are thus prevented from overheating, it being pointedout that the bottom region of the coolant housing 59 is disposed closerto wafer 18 than is window 68, so that thermal conduction through walls11 from the end portion of the cavity does not effect substantialheating of the cavity region adjacent wafer 18.

Because of the reflective characteristic of the interior surfaces of thekaleidoscope, the heating of a single wafer 18 to, for example, 1200°C., causes, over the time period indicated in FIG. 10, heating in FIG.10, heating of the exterior surface of apparatus 10 by only a smallamount, to substantially less than 150° F.

The cooling means for the flash lamps 47, shown at the upper portion ofFIG. 4, are similar to those for the CW lamps 17, and are not describedin detail. Also, the power supply for the flash lamps 47 may be ofseveral types known in the art, and is therefore not described herein.

Cooling means, corresponding to the housing 59, etc., are preferablyalso provided around the kaleidoscope 29 (bottom of FIGS. 1 and 2).

DESCRIPTION OF AUTOMATED APPARATUS

The apparatus schematically represented in FIG. 12 relates to theembodiment of FIGS. 4 and 11, but it is to be understood that theapparatus is also applicable to the embodiment of FIGS. 1-3 and 10. Inthe latter instance, the flash lamps and associated cooling means areomitted.

The upper kaleidoscope, numbered 10a (FIGS. 4-6) is held stationary bysuitable support means 70 connected to a housing, the latter beingindicated by the phantom lines 71 in FIG. 12. Coolant air for the flashlamps and kaleidoscope 10a is provided and withdrawn through conduits 72and 73 (FIG. 12) which extend through the housing 71.

The lower kaleidoscope 10 (FIGS. 4 and 5) is not held stationary butinstead actuated upwardly and downwardly between the illustrated closedposition and an open position (downwardly shifted) at which each quartzring 21 with wafer 18 thereon may be pivoted in a horizontal plane intoor out of the optical cavity. Referring to FIG. 12, a fluid-operatedcylinder 74 and associated guides 75 are employed for raising andlowering the kaleidoscope 10 and associated cooling apparatus. Theconduits 60 and 61 connecting to the coolant apparatus, and extending tothe exterior of housing 71, are made suitably flexible to permit thedescribed vertical shifting.

There are three shpport rings 21, mounted in a horizontal plane by meansof a rotating support apparatus 77 that is driven by an actuator 78.There are two loading cassettes 79 at one station within housing 71, andtwo unloading cassettes 80 at another station therein. Suitable pick andplace mechanisms, not shown, are provided to shift the wafers 18 intoand out of the loading and unloading cassettes 79 and 80, respectively.The provision of two cassettes 79, and two cassettes 80, permitscontinuous production-line operation.

The cassettes are introduced into and withdrawn from housings 71 through"airlocks" (not shown), and a desired atmosphere is provided within thehousing 71 and thus within the optical cavity. This atmosphere may beargon, nitrogen, helium, etc. (In different processes, the gas may beoxygen or various others.) The gas is supplied from a suitable source 81via a conduit 82. Direct connection of the gas source 81 to the opticalcavity may also (or alternatively) be effected, via conduits 83 and 84indicated in FIGS. 2 and 4-6, and gas flow is effected through suchconduits to increase cooling speed.

Continuous production-line operation may then be achieved by firstsignaling the actuator 74 to lower the bottom kaleidoscope 10, thensignaling the actuator 78 to rotate the apparatus 77 120° so that anuntreated wafer 18 is indexed into the space between the upper and lowerkaleidoscopes. Then, actuator 74 is signaled to raise kaleidoscope 10and thus cause opposed edges of the upper and lower kaleidoscopes 10aand 10 to meet each other and create a closed optical cavity in whichthe wafer 18 is disposed as shown in FIG. 4.

The radiant thermal sources 14 and 46 are then operated as describedabove, to create the combined isothermal and thermal flux annealing ofwafer 18. Thereafter, actuator 74 is actuated to lower the bottomkaleidoscope 10, and actuator 78 is signaled to rotate the apparatus 77and thus index the treated wafer 18 to the unloading station adjacentunloading cassettes 80 for unloading by the pick and place machine, notshown. The wafer is not shifted out of the cavity until it issufficiently cool that it will not be damaged.

The quartz handle 22 on support ring 21 extends through grooves(corresponding to grooves 23 in FIG. 1) in the upper edge of a wall 11of lower kaleidoscope 10 (FIG. 4). Such handle is connected to one ofthe arms of apparatus 77.

It is emphasized that the region surrounding wafer 18 is separated, bythe quartz windows 68 and 68a, from the end portions of thekaleidoscopes. There is little or no movement of the inert atmosphereadjacent wafer 18 when heating is occurring, this being desired becausesubstantially all heating is to be radiant, instead of conductive orconvective, for maximized uniformity of wafer temperature across thevarious diameters thereof. On the other hand, as stated previously,cooling rate may be increased by creating a flow of inert gas over thewafer during the cooling period.

There will next be indicated an automation apparatus for the embodimentdescribed relative to FIG. 7, the larger apparatus capable of heating,simultaneously and in one large cavity, a substantial number ofsemiconductor wafers. One such automation apparatus is a largemerry-go-round each arm of which supports--from a cavity-encompassingsquare element 77a--all eight (or other number) wafer-support rings 21.In another form, the wafer-support means move linearly instead ofrotationally, there being a "conveyor belt", each large "link" of whichis a square, that supports the inwardly-directed rings.

Relative to all embodiments, it is greatly preferred that the lowerportion of the optical cavity (that beneath the wafers or wafer) bepresent. Furthermore, it is preferred that such lower portion be closed(moved up) to the upper portion before each heating step. However, lesspreferably, instead of moving the entire lower cavity portion, upwardlymoving shutters or the like may be provided on the upper rim of astationary lower cavity. Even less preferably, there may be a gappresent between the lower and upper cavity portions during the heatingstep. Such a gap should be kept as small as possible, it beingunderstood that the wafer-support means may be so constructed as to bevery close to planar.

It is emphasized that, in all embodiments, the walls of the opticalcavities are relatively cool because of the high degree of reflectionfrom the reflective internal coatings. Nevertheless, for someapplications, means are provided to effect efficient cooling of thecavity walls. As an example, in a process where a workpiece is heatedcontinuously for one-half hour in an oxidizing atmosphere for thepurpose of achieving an oxide layer of desired thickness, the cavitywalls are water cooled by providing passages therethrough and effectingcontinuous flow of water through such passages.

DRAWINGS OF THE OPTICAL CAVITIES HAVING NON-SQUARE NESTINGCROSS-SECTIONAL SHAPES

FIGS. 13-15 all correspond to FIG. 3 but illustrate the three remainingcross-sectional shapes of the optical cavity or kaleidoscope, namely theregular hexagon, the equilateral triangle, and the rectangle. In FIGS.13-15, the numbers applied to the wafer, wafer support, reflectingcoatings and conduit are the same as in FIG. 3. The only structuraldifference between the embodiments of FIGS. 13-15 and that of FIGS. 1-3is the cross-sectional shape of the cavity. Thus, the walls of thehexagonal form (FIG. 13) are numbered 11d; the walls of the triangularform (FIG. 14) are numbered 11e; and the walls of the rectangular form(FIG. 15) are numbered 11f.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit and scope of thisinvention being limited solely by the appended claims.

What is claimed is:
 1. A method of rapid annealing dopant-implantedsemiconductor wafers, comprising:(a) employing CW lamp means and anintegrating light pipe to effect relatively uniform isothermal heatingof a dopant-implanted semiconductor wafer to a relatively hightemperature less than the melting point of the semiconductor materialforming said wafer, (b) causing the aspect ratio to be at least 1, and(c) maintaining said heating for a sufficient number of seconds toachieve rapid annealing.
 2. The invention as claimed in claim 1, inwhich the power to said CW lamp means is so controlled as to effect atemperature rise rate in the range of about 200° C. to about 500° C. persecond, and in which said high temperature is in the range of about1000° C. to about 1200° C.
 3. The invention as claimed in claim 2, inwhich said semiconductor wafer is silicon.
 4. A combination method ofrapid annealing a dopant-implanted semiconductor wafer, comprising:(a)employing CW lamp means and an integrating light pipe to effectrelatively uniform isothermal heating of a dopant-implantedsemiconductor wafer, (b) employing pulsed lamp means and an integratinglight pipe to effect substantially uniform thermal flux heating of thedopant-implanted surface region of said wafer after said isothermalheating step has generated an elevated temperature in the semiconductormaterial forming said wafer, and (c) causing the aspect ratio relativeto said CW lamp means and said pulsed lamp means to be at least
 1. 5. Acombination method of rapid annealing a dopant-implanted semiconductorwafer formed of silicon, said method comprising:(a) employing CW lampmeans and an integrating light pipe to effect relatively uniformisothermal heating of a dopant-implanted semiconductor wafer formed ofsilicon, to a temperature in the range of about 800° C. to about 1100°C., and (b) employing pulsed lamp means and an integrating light pipe toeffect substantially uniform thermal flux spike-heating of thedopant-implanted surface region of said wafer, to a temperature in therange of about 1200° C. to about 1400° C., after said isothermal heatingstep has generated the elevated temperature in the semiconductormaterial forming said wafer.
 6. A combination method of rapid annealinga dopant-implanted semiconductor wafer formed of gallium arsenide, saidmethod comprising:(a) employing CW lamp means and an integrating lightpipe to effect relatively uniform isothermal heating of adopant-implanted semiconductor wafer formed of gallium arsenide, to atemperature in the range of about 500° C. to about 600° C., and (b)employing pulsed lamp means and an integrating light pipe to effectsubstantially uniform thermal flux spike-heating of the dopant-implantedsurface region of said wafer, to a temperature in the range of about950° C. to about 1000° C., after said isothermal heating step hasgenerated the elevated temperature in the semiconductor material formingsaid wafer.
 7. A method of quick annealing the dopant-implanted surfaceof a semiconductor wafer having a diameter of at least 3 inches,comprising:(a) effecting substantially uniform isothermal heating of adopant-implanted semiconductor wafer, having a diameter of at least 3inches, across the entire area thereof by CW lamp means, (b) effecting,substantially concurrently with said step (a), substantially uniformthermal flux heating of the dopant-implanted surface of said wafer,across the entire area of said wafer, by pulsed means, and (c) effectingsaid substantially uniform isothermal heating and said substantiallyuniform thermal flux heating in an optical cavity, the aspect ratiorelative to said CW lamp means being at least 1,to thereby effect saidannealing.
 8. The invention as claimed in claim 7, in which the methodis so performed that the uniformity of the heating across the entirewafer is within plus or minus 2 percent, and in which said methodfurther comprises causing said optical cavity to have a substantiallynesting cross-sectional shape.
 9. A method of heating a large-diametersemiconductor wafer, comprising:(a) employing a kaleidoscope and asource of radiant thermal energy to apply to at least one surface of alarge-diameter semiconductor wafer a radiant thermal flux which issubstantially uniform across the entire wafer,said step (a) includingcausing said radiant source and wafer to be in said kaleidoscope, withsaid wafer spaced from said source a substantial distance axially ofsaid kaleidoscope, and further including causing the aspect ratio insaid kaleidoscope to be at least 1, and (b) employing said substantiallyuniform radiant thermal flux to heat said wafer at such temperatures andfor such time period as to achieve a desired process step relative tosaid wafer.
 10. The invention as claimed in claim 9, in which saidmethod further comprises causing said kaleidoscope to have a reflectiveend wall lying in a plane perpendicular to the axis of saidkaleidoscope.
 11. A method of heating a semiconductor wafer to achieve adesired effect, comprising:(a) providing, within an integrating lightpipe, incoherent lamp means having sufficient power to heat said waferto the desired temperature, and (b) providing a semiconductor wafer at adistance from said lamp means, longitudinally of said light pipe,sufficient that said integrating light pipe renders substantiallyuniform across said entire wafer the radiant thermal energy from saidlamp means, said distance being sufficient that the aspect ratio is atleast 1, and (c) effecting the desired heating of said wafer by saidsubstantially uniform radiant thermal energy.
 12. The method as claimedin claim 11, in which said lamp means comprises CW lamps.
 13. Theinvention as claimed in claim 11, in which said method further comprisesemploying both pulsed lamp means and CW lamp means as said lamp means,and effecting combination heating of said semiconductor wafer by both ofsaid lamp means, said CW lamp means being initially operated prior tooperation of said pulsed lamp means.
 14. The invention as claimed inclaim 11, in which said method further comprises employing akaleidoscope as said integrating light pipe.
 15. A method of heatinglarge-diameter semiconductor wafers, comprising:(a) providing akaleidoscope having a closed and internally-reflective end, andcontaining, relatively adjacent said end, a source of radiant thermalenergy, (b) employing said kaleidoscope to render substantially uniformthe radiation from said energy source, (c) disposing a large-diametersemiconductor wafer at a location where said energy is thus relativelyuniform, said location being such that the aspect ratio is at least 1,and (d) employing said uniform energy to heat said wafer substantiallyuniformly.
 16. The invention as claimed in claim 15, in which saidmethod further comprises effecting annealing by means of said heating.17. The invention as claimed in claim 15, in which said method comprisesdisposing said wafer internally of said kaleidoscope in spacedrelationship from the end of said kaleidoscope remote from said energysource, and further comprises employing a kaleidoscope wherein said endremote from said energy source is closed and internally reflective. 18.A method of heating a large-diameter semiconductor wafer, comprising:(a)providing first and second hollow integrating light pipes inaxially-adjacent end-to-end relationship, (b) effecting relative axialmovement between said light pipes to separate the adjacent end portionsthereof, (c) introducing a large-diameter semiconductor wafer betweenthe relatively adjacent ends of the thus-separated light pipes, untilsaid wafer is between the spaces within said light pipes, (d) effectingrelative axial movement of said light pipes to substantially close thespace therebetween, and (e) providing radiant thermal energy in both ofsaid light pipes to effect heating of said semiconductor wafer from bothsides thereof by radiant thermal energy that is substantially uniformacross said wafer.
 19. The invention as claimed in claim 18, in whichsaid method comprises employing light pipes that are closed at the endsthereof remote from said wafer, the closures being internallyreflective, and in which said method further comprises generating saidradiant thermal energy by lamps disposed within at least one of saidlight pipes at a distance spaced from said wafer sufficiently far thatthe resulting thermal flux is substantially uniform across said wafer.20. The invention as claimed in claim 18, in which said method isemployed to effect annealing of said wafer after a surface thereof hasbeen implanted with dopant.
 21. The invention as claimed in claim 18, inwhich each of said light pipes is a kaleidoscope.
 22. The invention asclaimed in claim 18, in which said method further comprises separatingsaid end portions as soon as said heating has been completed, to thusincrease the rate of cooling of said wafer.
 23. The invention as claimedin claim 22, in which said method further comprises flowing gas acrosssaid wafer as soon as separation occurs, to further increase coolingrate.
 24. A method of performing a process step in the manufacture of alarge-diameter semiconductor component, which comprises:(a) providing anoptical cavity having reflective interior surfaces so constructed andrelated that radiant heat energy from incoherent radiant-heat sourcemeans located in a region of said optical cavity is, by numerousreflections and re-reflections off said reflective interior surfaces,rendered uniform, within plus or minus a few percent, across alarge-diameter target area, (b) providing incoherent radiant-heat sourcemeans in said region of said cavity, (c) providing a large-diametersemiconductor component at said target area and in such orientation thatheat from said radiant-heat source means is uniformly distributed,within plus or minus a few percent, across said component, the aspectratio being at least 1, (d) providing a controlled atmosphere aroundsaid component, and (e) energizing said radiant-heat source means for atime period sufficient to heat said semiconductor component forperformance of a process step relative to said component.
 25. Theinvention as claimed in claim 24, in which said method further comprisescausing said reflective interior surfaces to be nondiffusely reflective.26. The invention as claimed in claim 24, in which said method furthercomprises causing said reflective interior surfaces to be diffuselyreflective.
 27. The invention as claimed in claim 24, in which saidmethod further comprises so relating said radiant-heat source means andsaid component that all radiant heat energy from said source means musttravel in said cavity, between said source means and said component, adistance in the range of from about one diameter of said cavity to atleast about two diameters of said cavity.
 28. The invention as claimedin claim 24, in which said method further comprises causing said cavityto have a substantially nesting cross-sectional shape.
 29. The inventionas claimed in claim 24, in which said method further comprises notlocating any hot plate near or in contact with said semiconductorcomponent.
 30. The invention as claimed in claim 24, in which saidmethod further comprises not locating any susceptor near or in contactwith said semiconductor component.
 31. The invention as claimed in claim24, in which said method further comprises not putting a diffuser in thepath of radiant heat from said source means to said semiconductorcomponent, and not contacting said component with any susceptor or hotplate.
 32. The invention as claimed in claim 24, in which said methodfurther comprises causing said semiconductor component to be alarge-diameter semiconductor wafer.
 33. The invention as claimed inclaim 24, in which said method further comprises causing said controlledatmosphere to be a gas selected from a group consisting of argon,helium, oxygen, nitrogen, and mixtures thereof.
 34. The invention asclaimed in claim 24, in which said method further comprises causing saidsemiconductor component to be a large-diameter semiconductor waferimplanted with dopant, and in which said process step is annealing ofsaid wafer.
 35. The invention as claimed in claim 24, in which saidmethod further comprises causing said semiconductor component to be asemiconductor wafer having a layer of refractory metal thereon, and inwhich said process step is silicide formation.
 36. The invention asclaimed in claim 24, in which said method further comprises causing saidsemiconductor component to be a semiconductor wafer, and in which saidmethod further comprises effecting said heating in the presence of a gasselected from a group consisting of oxygen, nitrogen, and mixturesthereof, and in which said process step is formation of an insulating ordielectric layer.
 37. A method of semiconductor-wafer heating,comprising:(a) providing an optical cavity having a substantiallynesting cross-sectional shape, and having sidewalls all of which arehighly reflective on the interior surfaces thereof, (b) providing asource of radiant heat energy within said optical cavity, (c) supportinga semiconductor wafer in said cavity and in spaced relationship fromsaid energy source, at such location that the radiant energy from saidsource, and passing through said optical cavity, will strike and heatsaid wafer, and (d) causing the aspect ratio in said cavity to be atleast
 1. 38. The invention as claimed in claim 37, in which said methodfurther comprises providing said source of radiant heat energy in theform of a source of incoherent light.
 39. The invention as claimed inclaim 37, in which said method further comprises causing said interiorsurfaces of the walls of said cavity to be nondiffusely reflective. 40.The invention as claimed in claim 37, in which said method furthercomprises causing said interior surfaces of the walls of said cavity tobe diffusely reflective.
 41. The invention as claimed in claim 37, inwhich said method further comprises causing the aspect ratio in saidcavity to be about
 2. 42. The invention as claimed in any of claims 28,or 37-40, inclusive, or 41, in which said nesting cross-sectional shapeis a square.
 43. A method of performing a process step relative to asemiconductor wafer, which comprises:(a) providing an integrating lightpipe, (b) effecting isothermal heating of a semiconductor wafer byemploying a radiant thermal source disposed in said light pipe, theaspect ratio being at least 1, and (c) effecting pulse heating of atleast one surface of said wafer while it is hot as the result of saidisothermal heating.
 44. The invention as claimed in claim 43, in whichsaid method further comprises employing as said integrating light pipe alight pipe having a nesting cross-sectional shape.
 45. The invention asclaimed in claim 43, in which said method further comprise employing assaid integrating light pipe a kaleidoscope.
 46. A method of performingat least one step relative to semiconductor wafers, said methodcomprising:(a) providing an optical cavity having a nestingcross-sectional shape, and having a size sufficiently large to receive,in a plane perpendicular to the axis of said cavity, at least one of thesemiconductor wafers to be treated, said cavity having sidewalls, theinterior surfaces of all sidewalls of said cavity being caused to behighly reflective, (b) providing a bank of lamps in said cavity in aplane perpendicular to the axis of said cavity, (c) providingwafer-support elements in said cavity and shaped to be in onlysmall-area contact with a wafer, to support said wafer in a second planethat is perpendicular to said cavity axis and is spaced a substantialdistance from said first-mentioned plane, (d) causing the aspect ratioin said cavity to be at least 1, (e) providing light-transmissiveseparator means between said wafer-support elements and said lamps, (f)disposing a semiconductor wafer on said wafer-support elements, (g)providing a controlled atmosphere around said wafer, on the side of saidseparator means remote from said lamps, (h) energizing said lamps toheat said wafer, and (i) de-energizing said lamps to cause said wafer tocool.
 47. The invention as claimed in claim 46, in which said methodfurther comprises causing said nesting cross-sectional shape to be asubstantial square.
 48. The invention as claimed in claim 46, in whichsaid method further comprises causing said separator means to be atransparent window.
 49. The invention as claimed in claim 46, in whichsaid method further comprises not using any diffuser or susceptorrelative to said heating of said wafer.
 50. The invention as claimed inany of claims 28, or 37-40, inclusive, or 41, or 46, in which saidnesting cross-sectional shape is a regular hexagon.
 51. The invention asclaimed in any of claims 28, or 37-40, inclusive, or 41, or 46, in whichsaid nesting cross-sectional shape is an equilateral triangle.
 52. Theinvention as claimed in any of claims 28, or 37, 41, or 46, in whichsaid nesting cross-sectional shape is a rectangle.
 53. The invenion asclaimed in any of claims 1, 4, 7, 9, 11, 15, 24, 37, 43, and 46, inwhich said aspect ratio is substantially greater than
 1. 54. A method ofheating a semiconductor wafer, said method comprising:(a) providing ahollow, integrating light pipe that causes the intensity of light tobecome relatively uniform across said pipe by reflections andrereflections as the light moves along said pipe, (b) providing lampmeans to create incoherent thermal radiation and to transmit suchradiation along said pipe, (c) supporting a semiconductor wafersurrounded by a controlled atmosphere in such position as to be struckby radiation radiated from said lamp means and integrated by said pipe,said supporting step (d) being such that the location of saidsemicondutor wafer is sufficiently far from said lamp means, in adirection perpendicular to a cross-section of said pipe, that said waferwill be relatively uniformly heated by radiation radiated from said lampmeans and integrated by said pipe, the aspect ratio being at least 1,and (d) providing a window between said semiconductor wafer and saidlamp means to contain said controlled atmosphere and maintain it out ofcontact with said lamp means.
 55. The method as claimed in claim 54, inwhich said method further comprises causing said integrating light pipeto be a kaleidoscope.
 56. A method of effecting double-sided andsubstantially uniform heating of a semiconductor wafer, said methodcomprising:(a) providing a kaleidoscope that causes the intensity oflight to become relatively uniform across said kaleidoscope byreflections and rereflections as the light moves along saidkaleidoscope, (b) closing one end of said kaleidoscope by aninwardly-facing reflective end-closure wall, (c) supporting asemiconductor wafer within said kaleidoscope at an intermediate regionthereof,said supporting step and said wafer respectively having suchcharacteristics and such size as to permit a substantial percentage ofradiant thermal energy within said kaleidoscope to pass along saidkaleidoscope past said wafer, the aspect ratio in said kaleidoscopebeing at least 1, and (d) supplying radiant thermal energy to saidkaleidoscope at a region farther from said reflective end-closure wallthan is said wafer,said method causing said wafer to be heatedrelatively uniformly on both sides,one side of said wafer being heatedby radiant thermal energy resulting from said step (d) and directed andintegrated by said kaleidoscope, the other side of said wafer beingheated by radiant thermal energy resulting from said step (d) anddirected and integrated by said kaleidoscope, then passing past saidwafer, then reflecting off said reflective end-closure wall, and thenbeing directed and integrated by said kaleidoscope back to said otherside of said wafer.
 57. A method of effecting double-sided andrelatively uniform heating of a semiconductor wafer, said methodcomprising:(a) providing a hollow, integrating light pipe that operates,by reflections and rereflections, to cause the intensity of light tobecome substantially uniform across said pipe as the light moves alongsaid pipe, (b) closing both ends of said pipe by inwardly-facingreflecting end walls, (c) supporting a semiconductor wafer, in acontrolled atmosphere, within said pipe at a region intermediate saidreflecting end walls,said wafer having such size and characteristics asto permit a substantial percentage of radiant thermal energy within saidpipe to pass along said pipe past said wafer, and (d) disposing lampmeans within said pipe relatively adjacent one of said reflecting endwalls, and radiating thermal energy from said lamp means both toward andaway from said one wall,said method effecting heating of said waferrelatively uniformly on both sides,one side of said wafer being heatedby radiant thermal energy from said lamp means and directed andintegrated by said pipe, another side of said wafer being heated byradiant thermal energy from said lamp means, directed and integrated bysaid pipe, and then passing past said wafer to engage the other of saidreflecting end walls, and then being directed and integrated by saidpipe back to said other side of said wafer, the aspect ratio in saidlight pipe being at least 1, said wafer being disposed a substantialdistance from each of said reflecting end walls.
 58. A semiconductorwafer-heating method, comprising:(a) providing a plurality ofinwardly-facing reflective surfaces in such relationship to each otheras to define an optical cavity having a substantially nestingcross-sectional shape, (b) disposing, in said optical cavity, lamp meansforming a source of radiant heat energy, and (c) supporting asemiconductor wafer in said cavity in spaced relationship from said lampmeans,the direction of said spacing being perpendicular to a crosssection of said cavity, said wafer-supporting step being such that whena wafer is thus supported, the radiant heat energy from said lamp meansand passing through said optical cavity will heat said wafer, the shapeof said optical cavity and the amount of such spacing of said wafer fromsaid lamp means being such that said wafer is substantially uniformlyheated, the aspect ratio in said optical cavity being at least
 1. 59.The method as claimed in claim 58, and further comprising providing aninwardly-facing reflective closure wall across said optical cavity onthe side of said lamp means remote from said wafer, and so orientingsaid last-mentioned wall that it is perpendicular to the axis of saidoptical cavity.
 60. The invention as claimed in claim 58, in which saidmethod further comprises causing said nesting cross-sectional shape tobe a square.
 61. The invention as claimed in claim 58, in which saidmethod further comprises causing said nesting cross-sectional shape tobe a regular hexagon.
 62. The invention as claimed in claim 58, in whichsaid method further comprises causing said nesting cross-sectional shapeto be an equilateral triangle.
 63. The invention as claimed in claim 58,in which said method further comprises causing said nestingcross-sectional shape to be a rectangle.
 64. The method as claimed inclaim 58, in which said method further comprises maintaining said waferin a controlled atmosphere, and providing a window to separate said lampmeans from said controlled atmosphere.
 65. A method heating a workpiece,which comprises:(a) defining an elongate optical cavity havingreflective inwardly-facing side walls and having a substantially nestingcross-sectional shape, (b) closing both ends of said cavity by closureshaving inwardly-facing reflective surfaces perpendicular to thelongitudinal axis of said cavity, and (c) providing incoherent sourcemeans of radiant-heat energy in a region of said cavity, and (d)supporting a workpiece at a target region in said cavity,the aspectratio in said cavity being at least 1, said method causing much of theincoherent radiant heat energy from said source means to be reflectedand rereflected many times before traveling from said source means tosaid workpiece, much of the incoherent radiant heat energy from saidsource means passing past said workpiece to one of said closures andthen being reflected back, and being reflected off said inwardly-facingside walls defining said optical cavity,said method thus effectingheating of said workpiece on both sides.